#include<iostream>
using namespace std;
class Square;
class Rectangle{
	int width,height;
	public:
		int area()
		{return (width*height);}
		void convert (Square a);
};

class Square{
	friend class Rectangle;
	private :
		int side;
		public:
			Square (int a):side(a){
			}
};
void Rectangle::convert(Square a){
	width=a.side;
	height=a.side;
}			
int main()
{
	Rectangle rect;
	Square sqr(4);
	rect.convert(sqr);
	cout<<rect.area();
	return 0;
}